Mixing system



H. N. JENKS MIXING SYSTEM March 18, 1952 2 SHEETS-SHEET 1 Filed Dec. 9, 1946 INVENTOR. Harry dank! BY W *flmm H. N. JENKS MIXING SYSTEM March 18, 1952 2 SHEETS-SHEET 2 Filed Dec. 9, 1946 woo INVENTOR. Harry M Jen/r:

Patented Mar. 18, 1952 UNITED STATES PATENT OFFICE 2,589,261 MIXlNG SYSTEM Harry N. J enks, Palo Alto, Calif.

Application December 9, 1946, Serial No. 715,109

3 Claims. 1

This invention relates to a mixing system of the same'general character as described in my Patent No. 1,902,078 of March 21, 1933, and which is highly useful for processing sewage and industrial wastes as well as for intimately mixing other liquids.

The operation of the system disclosed in the patent above referred to was thought to depend upon the use of mixing tanks of graded sizes, each provided with a conical bottom. From a standpoint of economy these structural requirements are objectionable, for the cost offabricating' conical bottomed tanks of different sizes greatly exceeds the cost of fabricating straight bottomed tanks all of an identical size.

In general, then, the object of this invention is the provision of a method of so operating a system of the character disclosed in said patent that the non-uniform conical bottomed tanks therein used can be replaced by straight bottomed tanks of uniform size.

More specifically, the object of this invention is the provision of a method of so operating a system of the character in question that a predetermined optimum ratio between the rates at which the influent is mixed or circulated within each tank is maintained, and that a predetermined and optimum rate of recirculation of influent between the two or more tanks of the system is maintained.

Referring to the drawings: I Fig. 1' is a top plan view of a two-tank mixin system embodying the objects of my invention.

Fig. 2 is a vertical section of the system shown in Fig. 1 taken on the section line 2--2 thereof.

Fig. 3 is a diagrammatic top plan view of a three-tank mixing system embodying the objects of my invention.

Fig 4 is a fragmentary detail of an air-lift which can be substituted for the screw pump shown in Figs. 1 and 2.

The system as shown in Figs. 1 and 2 comprises a primary tank I and a secondary "tank 2. Provided adjacent the upper periphery of the primary tank I 'is an influent inlet 3, and provided on. the bottom wall of the secondary tank 2 is an eiiluent discharge outlet 4. Disposed between the primary and secondary tanks I and 2 is a common conduit or riser 5 communicating at its lower end through a primary lower conduit or lateral 6 with the central bottom zone I of the primary .tank I, and communicating through a lower secondary conduit or lateral 8 with the lower central zone e of; the secondary tank 2. Provided adjacent the ,upper end of the riser 5 is an upper primary lateral II communicating with a tangential inlet I2 formed in the periph cry of the primary tank I. Also provided adjacent the upper end of the riser 5 on a common level with the lateral II is an upper secondary lateral I3 communicating with a tangential inlet IA formed in the secondary tank 2.

Mounted adjacent the upper end of the riser 5 is a variable speed drive unit I5, including a shaft which is provided with a bevel gear I511. Mounted within the riser 5 and coaxial therewith is a shaft I6, and formed thereon is a pump screw I'I forming with the riser 5 a screw conveyor pump. Keyed to the upper end of the shaft I6 is a bevel gear I3 in mesh with the bevel gear Ilia.

Since the operation of this system depends upon recirculating the influent through the primary and secondary tanks at predetermined optimum rates of flow, the cross-sectional areas of the lower laterals 6 and 8 should be substantially identical and, likewise, the cross-sectional areas of the upper primary and secondary laterals II and I3 should be identical, and likewise the tangential inlets I2 and I4. Otherwise gates or valves should be included in these conduits for controlling the rates'of flow therethrough.

In the operation of this device influent is fed to the primary tank I through the inlet 3 at a rate Q, and after the two tanks are filled to a common level above that of the upper primary and secondary laterals I I and I3, effluent is continuously discharged from the secondary tank 2 through the outlet 4 at the same rate Q. The pump screw I! is then rotated at such a rate that. it will pump influent from the primary and secondary tanks I and 2 through the riser 5 at the rate of 3Q. The rate at which the influent from the primary tank I passes through the bottom primary lateral 6 should then be 2.5Q and the rate at which influent passes through the lower secondary lateral 8 should be .5Q. The combined and admixed influent passing upwardly through the riser 5 then splits equally through the upper laterals II and I3, the influent passing tangentially into each tank at a rate of 1.5Q.

I Although there may be some latitude as to these rates, it is essential that the rate at which the influent passes from the secondary tank 2 through the bottom secondary lateral 8 be not less than .5Q, for otherwise the system would be short-circuited and some influent from the primary tank would pass through the bottom pri-- mary lateral 6 into the bottom secondary lateral 8.

As clearly shown in Figs. 1 and 2, the tangential discharge of the infiuent from the upper laterals I I and I3 respectively into the circular, specifically the cylindrical walls, primary and secondary tanks I and 2 causes the fluid in each tank to swirl bodily in a horizontal plane so as to produce a vortex 2I in the upper strata of the fluid contained in the primary tank and a somewhat smaller vortex 22 in the upper strata of the liquid contained in the secondary tank 2. In addition to this horizontal bodily swirl of the fluid in each tank, two radially transverse spirals are produced in each tank as diagrammatically indicated in Fig. 2, one in the upper half of the infiuent and one in its lower half. In the upper half a current is set up which moves from the center outwardly and slightly upwardly along and within the upper strata and then downwardly and inwardly toward the center along a central imaginary plane of cleavage. In the lower half of the tank this pattern is again duplicated, but in the opposite direction, so that midway between the bottom and top of'the tank these two currents diverge as they approach the walls of the tank, thereby causing an intimate admixture of the adjacent influent strata. Some of the influent passing upwardly through the riser from the primary tank is discharged through the tangential inlet I4 into the secondary tank 2, and likewise some of the infiuent from the secondary tank passing upwardly through the riser 5 finds its way to the tangentialoutlet I2 into the primary tank. It will therefore be seen that not only is there a mixing of the infiuent in each tank at a predetermined'and optimum rate but, in addition, there is I a recirculation of the influent from each tank to the other and a mixing of both infiuents as they pass through the riser 5 at a predetermined and optimum rate. As is well known in the sewage disposal industry, it is desirable to form and retain large fiocs of sewage and to avoid the breaking down of such flocs for the reason that thesubsequent separation of the liquid and solid contents of the sewage can be thereby better effected. By selecting the proper rate Q at which the sewage is delivered to the primary tank I and at which the resulting effluent is discharged from the secondary tank 2, it is possible in a system of this kind to so mix and treat the sewage that iarge fiocs can be formed and retained in the sys- "If desired, the screw pump shown in Figs. 1 and 2 can be replaced by an air-lift such as diagrammatically illustrated in Fig. 4. The air-lift shown in this figureincludes a chamber 23 located at the juncture of the primary and secondary laterals ea and 8a in vertical alignment with the commen riser 5a. Disposed over thechamber 23 is a perforated plate 24, and located within the chamber 23 below the plate 24 is a source 25 of air under suitable pressure, from which air passes upwardly through the plate 24 to lift and aerate the columnof influent' above it. The use of an airlift ill Connection with the treatment of sewage has advantages over and above the use of a screw pump, for the air not only serves to move the sewage upwardly through the common riser 5a but at the same time it supplies the required oxygen demand.

In Fig. 3 a mixing system involving the use of three tan-ks has been diagrammatically illustrated, although the number of tanks used can be extended indefinitely. This system in principle is-ide'ntical to the system shown in Figs. 1 and 2, and includes identical straight bottomed mixing tanks 26, 21 and 28. Located between the tanks 26 and 21 is a common riser 29, and located between tanks 21 and 28 is a common riser 3|. Communicating between the lower central zones of the tanks 26 and 21 and the bottom of the riser 29 are bottom laterals 32 and 33. Similarly, bottom laterals 34 and 35 establish communication between the central bottom zones of the tanks 21 and 28 and the lower end of the common riser 3|. The upper end of the riser 29 recir'culates infiuent into the upper end of the tank 26 through a tangential lateral 36 and into the upper end of the tank 21 through a tangential lateral 31. Similarly, eflluent passing upwardly through the riser 3| is delivered respectively and tangentially to the upper portions of the motor driven tanks 21 and 28 through laterals 38 and 39. Associated with each riser is a suitable pump 42 of the character previously described.

In this system, as in the one previously described, influent is delivered to the first tank 26 at a rate Q and discharged from the bottom of the last tank 28 through an outlet 4| at the same rate. Influent from the bottom of the tank 26 is delivered to the riser 29 at a rate 2.56), and infiuent from the tank 21 is delivered to the riser 29 at a rate of .562. Influent therefore passes upwardly through the riser at the rate of 3Q and is split equally at rates 1.5Q between the two upper laterals 36 and 31. The same rates obtain with respect to the tanks 21 and 28. As shown in Fig. 3, duplicate and symmetrical sets of risers and upper and lower laterals can be used.

For mixing alone, I have found that the requirements of satisfactory mixing velocities and low power consumption are best met by means of a low-head high-capacity pumping unit. However, since in sewage work it is essential to avoid the disintegration of the relatively fragile fioc resulting from chemical coagulation, standard types of pumps are not suitable in this type of system. For this reason care should be taken to use either a screw-conveyor pump such as above described or an air-lift if aeration is required.

Although the operation of my system does not depend upon the use of tanks of any specific dimensions, the following dimensions are given as illustrative of a full-scaleinstallation having a capacity of one million gallons per day.

Two circular fiat bottomed mixing tanks each having a diameter of 16'6" and a water depth of l0'3";

One screw-conveyor pump having a diameter of 24" and a pitch of 9";

One variable speed drive unit in which the speed range of the drive unit is from 76 R; P. M: to 304 R. P. M., and in which the speed range of the pump shaft is from 30.4 R. P. M. to 121.6 R. P. M.

In a system having units of the above dimensions, the total mixing period at one million gallons per day should be about 4'1 minutes. A pump speed of about 64 R. P. M. should produce a rate of flow (Q) through the system of about 350 gallons per minute; With this rate of flow through the system, the theoretical rate of recirculation of the influent should be about 1130 gallons per minute, and the theoretical recirculation ratio between the primary and secondary tanks should be about 3' to 1. The pump should havea capacity of about 2100 gallons per minute.

From the above description it will be seen that'I'have provided an extremely eflicient system and one which obviates the use of tanks of graded sizes and which are provided with conical bottoms. Although in describing this system particular reference has been made to its use in the sewage disposal field, it can be used to advantage in other fields where a comparable mixing action is desired.

I claim:

1. The method of operating a mixing system wherein primary and secondary mixing tanks having straight bottoms and cylindrical walls are connected at their central bottom zones with a common riser, said riser being provided at its upper-end with primary and secondary laterals communicating with said tanks through tangential outlets at a common level, and wherein said secondary tank is provided on its bottom with an efiluent discharge outlet leading from a low interior region proximate the marginal walls of the tanks; comprising: delivering influent to and into the upper interior portion of said primary tank and discharging efiluent from said discharge outlet at a rate Q; pumping infiuent from the bottom of said primary tank through said riser at a rate substantially equal to 2.5Q; simultaneously pumping infiuent from the bottom of said secondary tank through said riser at a rate substantially equal to but not less than .5Q; and causing substantially equal quantities of the influent passing through said riser to pass through said laterals and tangential outlets into said primary and secondary tanks respectively at rates substantially equal to 1.5Q.

2. The method of operating a mixing system wherein primary and secondary straight bottomed circularly walled mixing tanks of substantially identical dimensions are connected at their central bottom zones with a common riser, said riser being provided at its upper end with primary and secondary laterals communicating with said tanks through tangential outlets at a common level, and wherein said secondary tank is provided on its bottom with an effluent discharge outlet leading from a low region near the circular wall; comprising: delivering infiuent to said primary tank and discharging effluent from said discharge outlet at a rate Q; pumping influent from the bottom of said primary tank through said riser at a rate substantially equal to 2.5Q; simultaneously pumping infiuent from the bottom of said secondary tank through said riser at a rate substantially equal to but not less than .563; and causing substantially equal quantities of the infiuent passing through said riser to pass through said laterals and tangential outlets into said primary and secondary tanks respectively at rates substantially equal to 1.5Q.

3. The method of operating a mixing system including first, second and third mixing tanks wherein said first and second tanks are connected at their central bottom zones with a first riser, said riser being provided at its upper end with first and second laterals communicating respectively with said tanks through tangential outlets at a common level, wherein said second and third tanks are connected at their central bottom zones with a second riser and wherein at least the third tank has a straight bottom with a cylindrical marginal wall rising therefrom, said second riser being provided at its upper end with third and fourth laterals communicating respectively with the said second and third tanks through tangential outlets at a common level, and wherein said third tank is provided on its bottom with an efiluent discharge outlet leading from a region proximate the marginal wall; and comprising: delivering influent to said first tank and discharging effiuent from said discharge outlet ata rate Q; pumping infiuent from the central bottom zone of said first tank through said first riser at a rate substantially equal to 2.5Q; simultaneously pumping infiuent from the bottom central zone of said second tank through said first riser at a rate substantially equal to but not less than .5Q; simultaneously pumping infiuent from the bottom central zone of said second tank through said second riser at a rate substantially equal to 2.5Q; simultaneously pumping infiuent from the bottom central zone of said third tank through said second riser at a rate substantially equal to but not less than .5Q; causing the infiuent passing upwardly through said first riser to flow at equal rates through said first and second laterals respectively into said first and second tanks; and simultaneously causing the influent flowing upwardly through said second riser to flow at equal rates respectively through said third and fourth laterals into said second and third tanks at a rate substantially equal to 1.5Q.

HARRY N. JENKS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,727,152 Winkler Sept. 3, 1929 1,902,078 Jenks Mar. 21, 1933 2,096,728- Bighouse Oct. 26, 1937 2,346,366 Durbin, 3rd Apr. 11, 1944 2,421,191 Durbin, 3rd. Mar. 27, 1947 

